Structure and method for multi-ports optical apparatus

ABSTRACT

The present invention describes a structure and method for a multi-ports WDM device for compensating the filter distortion while reducing insertion loss. The multi-ports WDM device comprises a 4-fiber collimator having a grin lens and a 2-fiber collimator having a lens where the focal plane of the second lens is shorter than the focal plane of the first grin lens Ands with aspheric surface. When a light signal travels through the first lens in the 4-fiber collimator to a filter, the film on the filter causes distortion to the light signal resulting in a large insertion loss. To compensate for the insertion loss, the lens on the 2-fiber collimator has a aspheric function and a shorter focal plane than the grin lens on the 4-fiber collimator. The type of grin lens used in the 4-fiber collimator is different than the lens used in the 2-fiber collimator. Effectively, the lens in the 2-fiber collimator operates to de-focus a light signal relative to the grin lens in the 4-fiber collimator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application relates to a concurrently filed U.S. patent applicationSer. No. 11/247,779, entitled “Method for Assembly of Multi-PortsOptical Apparatus” by Xuehua Wu et al., filed on Oct. 11, 2005, owned bythe assignee of this application and incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates generally to optical technologies and moreparticularly to an optical Wavelength Division Multiplexing (WDM)devices with multiple ports.

2. Description of Related Art

Fiber optic networks are becoming increasingly popular for datatransmission due to their high speed and high data capacitycapabilities. Multiple wavelengths may be transmitted along the sameoptical fiber. This totality of multiple combined wavelengths comprisesa single composite transmitted signal. A crucial feature of a fiberoptic network is the separation of the optical signal into its singlewavelengths, or “channels”, typically by a dense wavelength divisionmultiplexer. This separation must occur in order for the exchange ofwavelengths between signals on “loops” within networks to occur. Theexchange occurs at connector points, or points where two or more loopsintersect for the purpose of exchanging wavelengths.

Add/drop systems exist at the connector points for the management of thechannel exchanges. The exchanging of data signals involves theexchanging of matching wavelengths from two different loops within anoptical network. In other words, each signal drops a channel to theother loop while simultaneously adding the matching channel from theother loop.

Traditional methods used by dense wavelength division multiplexers inseparating an optical signal into its single channels include the use offilters and fiber gratings as separators. A “separator,” as the term isused in this specification, is an integrated collection of opticalcomponents functioning as a unit which separates one or more channelsfrom an optical signal. Filters allow a target channel to pass throughwhile redirecting all other channels. Fiber gratings target a channel tobe reflected while all other channels pass through. Both filters andfiber gratings are well known in the optical art.

In a conventional solution, a WDM device comprises two collimators whereboth collimators employ the same type of grin lens for processing alight signal. While this structure may provide sufficient performancefor a coarse wdm as well as 400 GHz and 200 GHz filter, as the level ofthe filter increases, the coupling effect between the two collimators inthe WDM device will likely produce a significant amount of distortion,resulting in poor insertion loss. Accordingly, it is desirable to have aWDM device that compensates for filter distortion, thereby reducing theamount of insertion loss.

SUMMARY OF THE INVENTION

The present invention describes a structure and method for a multi-portsWDM device for compensating the filter distortion while reducinginsertion loss. The multi-ports WDM device comprises a 4-fibercollimator having a first type of grin lens and a 2-fiber collimatorhaving a second type of grin lens where the focal plane of the secondtype of grin lens is a different type of design from the first type ofgrin lens in the 4-fiber collimator. When a light signal travels throughthe first grin lens in the 4-fiber collimator to a filter, the film onthe filter causes distortion to the light signal resulting in anundesirable and large insertion loss. To compensate for the insertionloss, the second type of grin lens on the 2-fiber collimator has ashorter focal plane and aspheric function relative to the first type ofgrin lens in the 4-fiber collimator. Suitable selections of the secondtype of grin lens include a gradium lens, an aspheric lens, and a grinlens that provides a shorter focal plane than the first grin lens. Othertype of lens that has the characteristic of a shorter focal plane may beused without departing from the spirits of the present invention.Therefore, the type of grin lens used in the 4-fiber collimator isdifferent than the grin lens used in the 2-fiber collimator.Effectively, the grin lens in the 2-fiber collimator operates tode-focus a light signal relative to the grin lens in the 4-fibercollimator. One suitable implementation of the second type of grin lensin the 2-fiber collimator is a gradium lens.

Broadly stated, claim 1 recites a method for assembling a multi-port WDMdevice having a grin lens having a first principle face and a secondprinciple face, that comprises assembling a m-fiber collimator (m is aneven integer number), comprising: attaching a filter to the secondprinciple face of the grin lens; attaching a m-fiber pigtail to thefirst principle face of the grin lens; and placing a glass tube over theattached m-fiber pigtail, the grin lens, and the filter, the glass tubeextending along the surface of the m-fiber pigtail; assembling a n-fibercollimator (n=m/2), comprising: placing a second glass tube over a lensand extending beyond the lens; and inserting a n-fiber pigtail into theglass tube and attaching the n-fiber pigtail to the lens.

Advantageously, the present invention compensates for the insertion losscaused by a filter distortion when a light signal travels through thegrin lens in a first collimator, which allows the use of a thickercoated film filter for the design in a multi-ports WDM device. Anotheradvantage of all glass packaging WDM device is the desirablecharacteristics in the parameter of temperature dependent loss (TDL),saving the materials and the time period for development of WDM devicerelative with metal soldering WDM devices.

The other structures and methods regarding to the present invention aredisclosed in the detailed description below. This summary does notpurport to define the invention. The invention is defined by the claims.These and other embodiments, features, aspects, and advantages of theinvention will become better understood with regard to the followingdescription, appended claims and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial diagram illustrating a 4-fiber collimator forassembly in a six-ports WDM device in accordance with the presentinvention.

FIG. 2 is a pictorial diagram illustrating a 2-fiber collimator forassembly in the six-ports WDM device in accordance with the presentinvention.

FIG. 3 is a pictorial diagram illustrating the six-ports WDM deviceassembled with the 4-fiber collimator coupled to the 2-fiber collimatorin accordance with the present invention.

FIG. 4 is a pictorial diagram illustrating the WDM device with adistorted beam projected from a filter in the 4-fiber collimator that iscompensated by a lens in the 2-fiber collimator in accordance with thepresent invention.

FIG. 5A is a side view illustrating a 4-ports WDM device in accordancewith the present invention; FIG. 5B is a pictorial diagram illustratinglight signal projections from the 4-port input to a filter in accordancewith the present invention.

FIG. 6 is a side view illustrating a 6-ports pigtail-collimator in a 9port WDM device in accordance with the present invention.

FIG. 7 is a side view illustrating an 8-ports pigtail-collimator in a 12port WDM device in accordance with the present invention.

FIG. 8 is a pictorial diagram illustrating a glass package of the 6-portWDM device structure in accordance with the present invention.

FIG. 9 is a flow diagram illustrating the process in the assembly of theglass package in the 6-port WDM device structure in accordance with thepresent invention.

FIGS. 10A–10D are pictorial diagrams illustrating the process steps inthe assembly of the 4-fiber collimator in accordance with the presentinvention.

FIGS. 11A–11C are pictorial diagrams illustrating the process steps inthe assembly of the 2-fiber collimator in accordance with the presentinvention.

Reference symbols or names are used in the Figures to indicate certaincomponents, aspects or features therein, with reference symbols commonto more than one Figure indicating like components, aspects of featuresshown therein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

Referring now to FIG. 1, there is shown a pictorial diagram illustratinga 4-fiber collimator 100 for assembly in a six-port WDM device 300, asshown in FIG. 3. The 4-fiber collimator 100 comprises a 4-fiber pigtail110, a grin lens 120 and a filter 130. The 4-fiber pigtail 110 has fourports on one side and adjoins on the other side to the grin lens 120with the use of an epoxy 115 a and an epoxy 115 b. The grin lens 120 inturn adjoins to the filter 130 with an epoxy 125 a and an epoxy 125 b onbottom. In this embodiment, a short glass tube 140 with a hollow core isused to wrap around a portion of the 4-fiber pigtail 110. One ofordinary skill in the art should recognize that a different length ofglass tube, or other type of materials, such as metal, can be used towrap around all, more than, or less than the 4-fiber pigtail 110.Alternatively, the filter 130 can be implemented as a filter chip.

In FIG. 2, there is shown a pictorial diagram illustrating a 2-fibercollimator 200 for coupling to the 4-fiber collimator 100 for assemblyin the six-ports WDM device 300. The 2-fiber collimator 200 comprises alens 210, a 2-fiber pigtail 220, and a glass tube 230. The lens 210 ispreferably selected to have aspheric function and a shorter focal planethan the grin lens 120. A suitable example of the lens 210 is a gradiumlens. An optional glass tube 230 with a hollow core can be used to wraparound the 2-fiber pigtail 220. In this embodiment, the optional glasstube 230 extends across the body of the lens 210 and the two-fiberpigtail 220. The short glass tube 140 has a shorter tube length thatextends across the 4-fiber pigtail relative to the glass tube 230.

When applying an epoxy between the housing glass tube 310 and the shortglass tube 140, and when applying an epoxy between the housing glasstube 310 and the glass tube 230, an UV light is directed toward theepoxy areas followed by hot temperature baking, resulting in curing ofepoxy areas without affecting the original alignment or the opticalperformance including insertion loss.

FIG. 3 is shown a pictorial diagram illustrating the assembled six-portsWDM device 300 comprising the 4-fiber collimator 100 and the 2-fibercollimator 200. If a thin film filter is implemented in the filter 130,an optical signal is likely to be able to maintain the integrity of theoriginal light signal when traveling through the fiber collimator 100.However, when the film thickness increases on the filter 130, such asmore than 100 GHz coating filter, then the optical signal beam shapewill likely be distorted by the filter 130 when the light beam shapetravels from the 4-fiber collimator 100 to the 2-fiber collimator 200.To compensate for the distortion that may be caused by the filter 130,the lens 210 used in the 2-fiber collimator 200 is preferably differentfrom the grin 120 that is used in the 4-fiber collimator 100.Preferably, the aspheric surface and the focal plane on the lens 220 isshorter than the focal plane on the grin lens 120 so that optical signaltraveling through the filter 130, even if distorted, is compensated bythe lens 210 and properly alignment processing.

The 4-fiber collimator 100 is placed adjacent to the 2-fiber collimator200 in a housing 310. The housing 310 can be selected as a glass packageor a soldering package. In the soldering package, the selected type ofmaterial is metal for the housing 310 with an interior stainless steeltubes (SST) 320 and 330. In the glass package, the selected type ofmaterial is glass, which does not need the stainless steel tubes 320 and330. Other types of materials can also be selected to manufacture thehousing 310 without departing from the spirits of the present invention.

In FIG. 4, there is shown a pictorial diagram illustrating an example ofa WDM device 400 with a distorted beam projected from a filter in afirst collimator 410 which is compensated by a different type of lens ina second collimator 450. The first collimator 410 comprises a first port415 and a second port 417 attached to a pigtail 420, which in turncouples to a first type of grin lens 430, which in turn couples to afilter 440 with a coating film, which in turn attaches to a substrate445. The second collimator 460, comprises a second type of lens 470, apigtail 480 and a third port 490. In this illustration, the filter 440selected in this design causes a beam distortion, which is shown in FIG.4 with a typical collimated beam 450 and distorted beams 451 a and 451 bextending outward from the side boundaries of the regular collimatedbeam 450. The second type of lens 470, however, has a wider receivingarea, shown here in a defocused beam shape rather than a typicalcollimated shape, for receiving both the regular projected beam 450 aswell as the distorted beams 451 a and 451 b.

Turning now to FIG. 5A, there is a perspective view illustrating a4-port pigtail collimator 500 comprising a first input port 510, asecond input port 520, a first reflection port 530 and a secondreflection port 540. An incoming light signal entering into the firstinput port 510 is reflected to the first reflection port 530. Similarly,the light signal entering into the second input port 520 will bereflected to the second reflection port 540. The light signalprojections for the two input ports 510 and 520 are further depicted ina graphical diagram in FIG. 5B. The light signal entering the firstinput port 510 is projected onto and reflected off a filter 550 to thefirst reflecting port 530, as indicated from a first arrow 515 from thefirst input port 510 and a second arrow 525 entering the firstreflecting port 530. As for the second input port 520, the light signalentering the second input port 520 is projected onto and reflected offthe filter 550 to the second reflecting port 540, as indicated from athird arrow 535 from the second input port 520 and a fourth arrow 545entering the second reflecting port 540. One of ordinary skill in theart should recognize that the present invention is applicable to othermulti-port pigtail device, such as a nine-port pigtail as shown in FIG.6 and a twelve-port pigtail as shown in FIG. 7.

Turning now to FIG. 8, there is shown a pictorial diagram illustrating aglass package of a 6-port WDM device structure 800. The two primarycomponents, the 4-fiber collimator 100 and the 2-fiber collimator 200are placed in a glass tube 810 for packaging. In this embodiment, the4-fiber collimator 100 is placed in the glass tube 140 first beforeinserting the glass tube 140 into the glass tube 810. The 2-fibercollimator 200 is placed in the glass tube 230 first before insertingthe glass tube 230 into the glass tube 810. An epoxy 820 a is used inthe left end as an adhesion to hold the glass tube 140 to the glass tube810. An epoxy 820 b is used in the right end as an adhesion to hold theglass tube 230 to the glass tube 810. And also an epoxy applied in thegap between the glass tube 810 and 140, as well as the glass tube 810and 230.

In FIG. 9, there is shown a flow diagram illustrating the assemblyprocess 900 in the assembly of the glass package in the 6-port WDMdevice structure 800. The 6-port WDM multi-port device 800 isconstructed mainly from two parts, the 4-fiber collimator 100 and the2-fiber collimator 200. In assembling the 4-fiber collimator 100, atstep 910, the filter 130 is attached to the grin lens 120 with anadhesive material, such as epoxy. At step 920, the 4-fiber pigtail 110is attached and aligned with the grin lens 120 and the filter 130. Atstep 930, the process 900 installs the glass tube 140 over the 4-fiberpigtail 110. As an alternative embodiment, a glass tube can be used inplace of the stainless steel tube for packaging the 4-fiber collimator100 and the 2-fiber collimator 200. Similarly, the assembly for theother part, the 2-fiber collimator 200, begins by placing the lens 210,such as a lens, in the glass tube 230 at step 950. At step 960, the2-fiber pigtail 220 is attached to the lens 210. The 4-fiber collimator100 having a first type of lens is aligned with a second type of lens inthe 2-fiber collimator 200 to produce the multi-ports WDM device 980.

When metal is selected for packaging the 4-fiber collimator 100 and the2-fiber collimator 200, the adhesive material used to hold the 4-fibercollimator 100 and the 2-fiber collimator 200 to the metal packaging issoldering. However, both collimators are needed to put on the stainlesssteel tubes as shown in FIG. 3. When glass is selected for packaging the4-fiber collimator 100 and the 2-fiber collimator 200, the adhesivematerial used to hold the 4-fiber collimator 100 and the 2-fibercollimator to the metal packaging is epoxy.

In FIGS. 10A–10D, there are shown pictorial diagrams illustrating theprocess steps in the assembly of the 4-fiber collimator 100. In thefirst step as shown in FIG. 10A, the grin lens 120 adjoins to the filter130 using an adhesive material such as epoxy. In the second step asshown in FIG. 10B, the 4-fiber pigtail 110 is adjoined to the grin lens120. In the third step, the short glass tube 140 with a hollow core isused to wrap around a portion of the 4-fiber pigtail 110, as shown inFIG. 10C. The 4-fiber collimator 100 is placed inside the housing 310 inthe fourth step as shown in FIG. 10D for soldeing type use.

FIGS. 11A–11C are pictorial diagrams illustrating the process steps inthe assembly of the 2-fiber collimator 200. In the first step as shownin FIG. 11A, the lens 210 is placed in the glass tube 230. In the secondstep as shown in FIG. 11B, the 2-fiber pigtail 220 is then attached tothe lens 210 and inside the glass tube 230. The 2-fiber collimator 200is subsequently placed inside the housing 310 (as shown in FIG. 3) inthe third step as shown in FIG. 11C, which can be selected as a glasspackage or a soldering package. In the soldering package, the selectedtype of material is metal for the housing 310 with an interior stainlesssteel tubes (SSD) 320 and 330. In the glass package, the selected typeof material is glass, which does not need the stainless steel tubes 320and 330.

Those skilled in the art can now appreciate from the foregoingdescription that the broad techniques of the embodiments of the presentinvention can be implemented in a variety of forms. Therefore, while theembodiments of this invention have been described in connection withparticular examples thereof, the true scope of the embodiments of theinvention should not be so limited since other modifications, whetherexplicitly provided for by the specification or implied by thespecification, will become apparent to the skilled practitioner upon astudy of the drawings, specification, and following claims.

1. A WDM device, comprising a m-fiber collimator having a first type ofgrin lens coupled to a filter, the m-fiber collimator receiving a lightsignal and propagating the light signal through the first type of grinlens and the filter, the first type of grin lens in the m-fibercollimator having a focal plane; a n-fiber collimator having a secondtype of grin lens, the second type of grin lens in the n-fibercollimator receiving the light signal propagating from the filter of them-fiber collimator, the second type of grin lens in the n-fibercollimator having a focal plane; and a first glass tube placed outsideof m-fiber collimator and coupling to the first type of grin lens forprocessing the light signal from the m-fiber collimator inside the firstglass tube to the grin lens, the m-fiber collimator including a 4-fiberpigtail inside the first glass tube for processing the light signal fromthe 4-fiber pigtail inside of the first lass tube; wherein the focalplane in the second type of grin lens of the n-fiber collimator isshorter than the focal plane in the first type of grin lens of them-fiber collimator for compensating the distortion caused when the lightsignal travels through the filter.
 2. The WDM device of claim 1, whereinthe grin lens in the n-fiber collimator comprises a gradium lens.
 3. TheWDM device of claim 1, wherein the grin lens in the n-fiber collimatorcomprises an aspheric lens.
 4. The WDM device of claim 1, wherein them-fiber collimator comprises a filter coupling to the grin lens forfiltering the light signal received from the grin lens.
 5. The WDMdevice of claim 4, wherein the filter is a 25 GHz, 50 GHz, or 100 GHzfilter.
 6. The WDM device of claim 1, wherein the n-fiber collimatorcomprises a 2-fiber pigtail coupling to a second glass tube forprocessing the light signal from the second glass tube to the 2-fiberpigtail.
 7. The WDM device of claim 1, wherein the combination of them-fiber collimator and n-fiber collimator produces a 6-ports WDM device.8. The WDM device of claim 1, wherein the combination of the m-fibercollimator and n-fiber collimator produces a 9-ports WDM device.
 9. TheWDM device of claim 1, wherein the combination of the m-fiber collimatorand n-fiber collimator produces a 12-ports WDM device.
 10. A method forprocessing a light beam in a multi-port device having a m-fibercollimator and a n-fiber collimator, comprising: receiving a light beamin a m-fiber collimator propagating the light beam from the m-fibercollimator inside a glass tube to a grin lens, the m-fiber collimatorincluding a 4-fiber pigtail inside the first glass tube for processingthe light signal from the 4-fiber pigtail inside the first glass tube,the grin lens in the m-fiber collimator having a focal plane; filteringthe light beam; and compensating the light beam through a grin lens in an-fiber collimator, the grin lens in the n-fiber collimator having afocal plane; wherein the focal plane in the grin lens in the n-fibercollimator is shorter than the focal plane in the grin lens of them-fiber collimator for compensating the distortion caused when the lightbeam travels through the filter.
 11. The method of claim 10, wherein thegrin lens in the n-fiber collimator comprises a gradium lens.
 12. Themethod of claim 10, wherein the grin lens in the n-fiber collimatorcomprises an aspheric lens.